Feature creap I guess, support for "every friday"
and "the first wednesday" in calender for regular 
jargon-bingo sessions.

Notes:
Mon Dec 20 13:07:37 EST 2004 rsc
    maybe we can find a more general way to do this


Reference: /n/sources/patch/applied/calendar
Date: Tue Jan  4 17:09:10 CET 2005
Reviewed-by: rsc

--- /sys/src/cmd/calendar.c	Tue Jan  4 17:09:10 2005
+++ /sys/src/cmd/calendar.c	Tue Jan  4 17:09:10 2005
@@ -14,12 +14,13 @@
 	Secondsperday = 24*60*60
 };
 
+Date *Base = nil;
 Biobuf in;
 int debug, matchyear;
 
-Date *dates(Date**, Tm*);
+void dates(Tm*);
 void upper2lower(char*, char*, int);
-void *alloc(unsigned int);
+void *emalloc(unsigned int);
 
 void
 main(int argc, char *argv[])
@@ -28,7 +29,7 @@
 	long now;
 	char *line;
 	Tm *tm;
-	Date *first, *last, *d;
+	Date *d;
 	char buf[1024];
 
 	ahead = 0;
@@ -50,26 +51,25 @@
 	/* make a list of dates */
 	now = time(0);
 	tm = localtime(now);
-	last = nil;
-	first = dates(&last, tm);
+	dates(tm);
 	now += Secondsperday;
 	tm = localtime(now);
-	dates(&last, tm);
+	dates(tm);
 	if(tm->wday == 6){
 		now += Secondsperday;
 		tm = localtime(now);
-		dates(&last, tm);
+		dates(tm);
 	}
 	if(tm->wday == 0){
 		now += Secondsperday;
 		tm = localtime(now);
-		dates(&last, tm);
+		dates(tm);
 	}
 	if(ahead){
 		now = time(0);
 		now += ahead * Secondsperday;
 		tm = localtime(now);
-		dates(&last, tm);
+		dates(tm);
 	}
 
 	for(i=0; i<argc || (i==0 && argc==0); i++){
@@ -88,7 +88,7 @@
 		while(line = Brdline(&in, '\n')){
 			line[Blinelen(&in) - 1] = 0;
 			upper2lower(buf, line, sizeof buf);
-			for(d=first; d; d=d->next)
+			for(d=Base; d; d=d->next)
 				if(regexec(d->p, buf, 0, 0)){
 					print("%s\n", line);
 					break;
@@ -114,18 +114,39 @@
 	"november",
 	"december"
 };
+char *nth[] = {
+	"first", 
+	"seccond",
+	"third",
+	"fourth",
+	"fifth"
+};
+char *days[] = {
+	"sunday",
+	"monday",
+	"tuesday",
+	"wednesday",
+	"thursday",
+	"friday",
+	"saturday"
+};
 
 /*
  * Generate two Date structures.  First has month followed by day;
  * second has day followed by month.  Link them into list after
  * last, and return the first.
  */
-Date*
-dates(Date **last, Tm *tm)
+void
+dates(Tm *tm)
 {
-	Date *first;
 	Date *nd;
-	char mo[128], buf[128];
+	char mo[128], day[128], buf[128];
+
+	if(utflen(days[tm->wday]) > 3)
+		snprint(day, sizeof day, "%3.3s(%s)?",
+			days[tm->wday], days[tm->wday]+3);
+	else
+		snprint(day, sizeof day, "%3.3s", days[tm->wday]);
 
 	if(utflen(months[tm->mon]) > 3)
 		snprint(mo, sizeof mo, "%3.3s(%s)?",
@@ -134,37 +155,50 @@
 		snprint(mo, sizeof mo, "%3.3s", months[tm->mon]);
 	if (matchyear)
 		snprint(buf, sizeof buf,
-			"(^| |\t)((%s( |\t)+)|(%d/))%d( |\t|$)(((%d|%d)( |\t|$))|[^0-9]|([0-9]+[^0-9 \t]))",
-			mo, tm->mon+1, tm->mday, tm->year+1900, tm->year%100);
+			"^[\t ]*((%s( |\t)+)|(%d/))%d( |\t|$)(((%d|%d|%02d)( |\t|$))|[^0-9]|([0-9]+[^0-9 \t]))",
+			mo, tm->mon+1, tm->mday, tm->year+1900, tm->year%100, tm->year%100);
 	else
 		snprint(buf, sizeof buf,
-			"(^| |\t)((%s( |\t)+)|(%d/))%d( |\t|$)",
+			"^[\t ]*((%s( |\t)+)|(%d/))%d( |\t|$)",
 			mo, tm->mon+1, tm->mday);
 	if(debug)
 		print("%s\n", buf);
 
-	first = alloc(sizeof(Date));
-	if(*last)
-		(*last)->next = first;
-	first->p = regcomp(buf);	
+	nd = emalloc(sizeof(Date));
+	nd->p = regcomp(buf);
+	nd->next = Base;	
+	Base = nd;
 
 	if (matchyear)
 		snprint(buf, sizeof buf,
-			"(^| |\t)%d( |\t)+(%s)( |\t|$)(((%d|%d)( |\t|$))|[^0-9]|([0-9]+[^0-9 \t]))",
-			tm->mday, mo, tm->year+1900, tm->year%100);
+			"^[\t ]*%d( |\t)+(%s)( |\t|$)(((%d|%d|%02d)( |\t|$))|[^0-9]|([0-9]+[^0-9 \t]))",
+			tm->mday, mo, tm->year+1900, tm->year%100, tm->year%100);
 	else
 		snprint(buf, sizeof buf,
-			"(^| |\t)%d( |\t)+(%s)( |\t|$)",
+			"^[\t ]*%d( |\t)+(%s)( |\t|$)",
 			tm->mday, mo);
 	if(debug)
 		print("%s\n", buf);
-	nd = alloc(sizeof(Date));
+	nd = emalloc(sizeof(Date));
+	nd->p = regcomp(buf);	
+	nd->next = Base;	
+	Base = nd;
+
+	snprint(buf, sizeof buf, "^[\t ]*every[ \t]+%s", day);
+	if(debug)
+		print("%s\n", buf);
+	nd = emalloc(sizeof(Date));
 	nd->p = regcomp(buf);	
-	nd->next = 0;
-	first->next = nd;
-	*last = nd;
+	nd->next = Base;	
+	Base = nd;
 
-	return first;
+	snprint(buf, sizeof buf, "[\t ]*the[\t ]+%s[\t ]+%s", nth[tm->mday/7], day);
+	if(debug)
+		print("%s\n", buf);
+	nd = emalloc(sizeof(Date));
+	nd->p = regcomp(buf);	
+	nd->next = Base;	
+	Base = nd;
 }
 
 /*
@@ -182,7 +216,7 @@
  * Call malloc and check for errors
  */
 void*
-alloc(unsigned int n)
+emalloc(unsigned int n)
 {
 	void *p;
 
--- /sys/man/1/calendar	Tue Jan  4 17:09:10 2005
+++ /sys/man/1/calendar	Tue Jan  4 17:09:10 2005
@@ -25,6 +25,10 @@
 "11 April",
 and
 "11 Apr".
+A special form may be used to represent weekly and
+monthly events:
+"Every Tuesday"
+"The third Wednesday"
 All comparisons are case insensitive.
 .PP
 If the